This invention relates to photographic apparatus and more particularly, it concerns automatic lens focusing systems for cameras.
Systems by which the objective lens of a camera may be focused on a subject automatically are disclosed in such prior publications as U.S. Pats. No. 3,522,764, No. 3,713,371, West German Pat. No. 864,048 and I.B.M. Technical Disclosure Bulletin, Volume 9, No. 7, December, 1966 pp. 744-745. With the exception of U.S. Pat. No. 3,713,371, the systems disclosed in these prior publications involve the transmission of ultrasonic energy toward a subject to be photographed and the reflection of such energy from the subject back to the camera. Characteristics including the time duration between energy transmission and reception are electronically processed to develop a control signal representative of the distance between the camera and the subject. The control signal is then used to operate a lens mount drive provided in the camera so that the lens will be positioned to focus the subject on the film plane of the camera. In the excepted U.S. Pat. No. 3,713,371, the distance between the camera and the subject is detected by a photoelectrically powered spacial frequency sensing device capable of generating a signal in response to the sharpness of an image formed by the camera lens when properly focused. The system is limited to use in relatively complex reflex type cameras in which the characteristics of focused image forming light passing through the lens is relied on to develop a signal indicative of camera subject range.
In a commonly assigned copending U.S. Application for patent Ser. No. 729,392, filed Oct. 4, 1976 by Juerg Muggli, there is disclosed an ultrasonic ranging system for a camera having a lens mount movable to a position at which a subject to be photographed is in focus. This system includes an ultrasonic transducer that responds to a keying pulse by transmitting a relatively short burst of frequency modulated ultrasonic energy, and a synchronized receiver for processing an echo signal produced by the transducer on receipt of an echo within a predetermined time interval following the transmission time of the burst. The receiver produces a range signal with a characteristic linearly related to the distance of a subject from a camera. Echo signals produced by the transducer are filtered by a variable filter operative in a manner to avoid the need for separate transmitting and receiving transducers. The receiver of the system includes a detector means responsive to the output of the filter for producing a range signal when the output exceeds a predetermined level. The timing of the range signal measured from the time of the keying pulse is representative of camera-subject distance.
The range finding systems of the prior art coupled with the current state of the electronics art, particularly as represented by the disclosure of the aforementioned copending U.S. application, make possible the mass production of relatively low cost cameras having automatic range finding systems. There is a need, however, for a combination of simplicity and reliability in a drive system capable of responding to the range indicating signal and adjustably positioning the camera objective lens to focus the subject properly on the film plane of the camera in a time interval commensurate with the time required to depress a camera shutter actuating button.